Your car sounds just about identical to one I'm working on right now, except for the 4 link and this one is a few percentage points lighter on the nose. That and it has a 900 horse SB2 in it. We're putting Strange DAs with 8" 350# springs on the front and 125# springs on the rear to try to calm the ladder bar suspension down. I'd like to have the front shocks in at about 9.75" with the spring compressed 2.5" or so. Front spring rates aren't as critical as rears, but I like to have them compressed a bit to make the front end a little more "lively" and control it with the shock. I'm going to put this thing together and on scales in the morning to see if my results match my arithmetic.

That 8" spring is compressed 1/2" when it's on that short shock with the spring seat all the way down. Then compress it another 1 1/2" to get the shock in at the correct length. My arithmetic says a 400 spring will be compressed ~2" at ride height. A 350 spring will need to be compressed ~2.5".

You mean a 1.90 in a Glide?